Module 07: Earth System Models

Climate models (also known as Earth system models) integrate our understanding of the basic physics and chemistry of the atmosphere, ocean, and land. They are used to explore scenarios of future climate change and impacts that would result from different levels of future emissions of CO2 and other greenhouse gases.  Climate models represent the entire world as a very large number of “grid boxes.” Each box has a single value of every variable that’s predicted (temperature, water, wind, etc) and mechanistic equations are used to advance the model forward in time. We use these models to “predict the past” from 1850 to now in order to evaluate their fidelity, and we use dozens of different models to do the simulations so that we can estimate uncertainties in the predictions. They work very well for the global average, but less well at smaller scales. We can’t predict economic, policy, and technological developments so instead we use a wide range of scenarios to define pathways of future emissions (Representative Concentration Pathways – RCPs). Each of these scenarios is then used to estimate future. 

Upon completion of this module you should be able to: 

1. Enumerate the three basic components of a climate model.
2. Discuss the concept of grid resolution in climate models, with examples.
3. Explain the use of hindcasting experiments and enumerate salient results from such experiments.
4. Explain the development and use of emissions scenarios in climate change assessments.
5. Describe the process by which global climate projections are produced.

• Module 7: Modeling Earth’s Climate System
• MODELS [Schmittner OER Ch 7]
• MODELING THE CLIMATE SYSTEM [Goose et al Open University Textbook, Chapter 3]
• Elsevier: Global Environmental Change: Riahi, K., et al (2015). Shared Socioeconomic Pathways and their energy, land use, and greenhouse gas emissions implications: An overview.

• Video 7.1: Earth System Models
• Video 7.2: Hindcasts for Model Evaluation
• Video 7.3 Emission Scenarios

Module 7: Earth System Models

1. Explain the difference between empirical and deterministic models.
2. List three main components of every global climate model. What do climate models predict well? What is not included in climate models?
3. Explain the difference between weather forecasting and climate projections as performed with modern numerical models.
4. What are grid cells as used in Earth system models? About how wide are the grid cells in most models used for projecting future climate?
5. Explain the use of “hindcasting” experiments used to evaluate the accuracy of global climate models and characterize the main conclusions of these studies.
6. Describe a climate phenomenon that global climate models predicted long before it was observed.
7. Describe the accuracy of geographic patterns of precipitation simulated by modern global climate models.
8. How are climate projections made for the 21^st Century (what steps are taken to produce the maps of projected changes)?
9. How are future emissions of greenhouse gases treated in global climate model simulations?
10. Emission scenarios for projection of future climate in models were formerly called Representative Concertation Pathways (RCPs) and are now called Shared Socioeconomic Pathways (SSPs). RCPs 2.6, 4.5, and 6.0 indicate that CO2 emissions will peak in which years and then decline thereafter?
    
11. Using the RCP8.5 high emissions scenario, what is the projected radiative forcing of climate in the year 2200?